Magnetic bubble devices with controlled temperature characteristics

Abstract

The temperature variation of the bubble collapse field of a class of garnet magnetic bubble layer materials is selected by control of octahedral site substitution during layer growth. This permits the growth of layers, whose temperature dependence of critical magnetic properties more closely matches the temperature dependence of available bias magnet materials, resulting in extended operating temperature range and/or wider operating margins (with attendant improvement in manufacturing yield). A preferred substitution species is lutetium, known as a dodecahedral site occupant, for which it has been determined that a significant and controllable octahedral occupancy can be produced by suitable choice of growth conditions.

What is claimed is: 
     
       1. A magnetic bubble device comprising a. a substrate supporting at least a first layer of an iron containing garnet possessing an uniaxial magnetic anisotropy perpendicular to the layer, which layer is capable of supporting magnetic bubbles which are stable and of a characteristic diameter in a temperature varying bias field over a temperature range, which anisotropy is predominantly a growth induced anisotropy produced by dodecahedral site substitution, which bias field is produced by a magnet adapted for maintaining the layer in the bias field throughout the temperature range, which bias field is less than a bubble collapse field at each temperature within the temperature range, and which bias field varies throughout the temperature range at an average rate, Δ;   b. generating means for generating the bubbles; and   c. propagating means for moving the bubbles in order to produce information processing characterized in that the iron garnet contains at least one member of the group consisting Lu, Yb, or Tm in octahedral sites, in a total relative molar concentration of from 0.01 to 0.2 per formula unit, such that the bubble collapse field of the garnet varies with temperature throughout the temperature range at an average rate of approximately Δ.   
     
     
       2. A device of claim 1 in which the composition of the first layer of iron garnet can be represented by the atomic formula:   (R1).sub.3.sub.-(a.sub.+b) (R2).sub.a.sub.+c (Ca,Sr).sub.b (Ge,Si).sub.b Fe.sub.5.sub.-(b.sub.+c) O.sub.12 ;     where (R1) is at least one member of the group consisting of Y, Gd, Sm or Eu; and (R2) is Lu, Yb or Tm.   
     
     
       3. A device of claim 2 in which a is from 0.1 to 2.95 and c is from 0.01 to 0.2. 
     
     
       4. A device of claim 3 in which (R2) is Lu. 
     
     
       5. A device of claim 4 in which the substrate is gadolinium gallium garnet and the composition of the first layer of the iron containing garnet can be represented by the atomic formula:   Y.sub.1.48 Lu.sub..29 Sm.sub..27 Ca.sub..96 Ge.sub..96 Fe.sub.4.04 O.sub.12 ;     where c is approximately 0.02, resulting in an average rate of change of bubble collapse field of approximately -0.2 percent per centigrade degree over the temperature range from -25° C to +50° C.   
     
     
       6. A device of claim 5 including a magnet consisting of barium ferrite adapted for maintaining the layer in a bias field which varies with temperature at an average rate of approximately -0.2 percent per centigrade degree over the temperature range from -25° C to +50° C. 
     
     
       7. A device of claim 4 in which the substrate is gadolinium gallium garnet and the composition of the first layer of the iron containing garnet can be represented by the atomic formula:   Y.sub.1.27 Lu.sub..45 Sm.sub..38 Ca.sub..9 Ge.sub..9 Fe.sub.4.1 O.sub.12 ;     where c is approximately 0.027, resulting in an average rate of change of bubble collapse field of approximately -0.2 percent per centigrade degree over the temperature range from 0° C to 100° C.   
     
     
       8. A device of claim 7 including a magnet consisting of barium ferrite adapted for maintaining the layer in a bias field which varies with temperature at an average rate of approximately -0.2 percent per centigrade degree over the temperature range from 0° C to 100° C.